1. Field of the Disclosure
The present invention relates to turbopumps, and in particular turbopumps for feeding the combustion chambers of rocket engines with fuel and/or oxidizer propellants, and more particularly with cryogenic propellants.
2. Description of the Related Art
A turbopump comprises a pump and a turbine connected together by a common rotary shaft so that the rotation of the turbine rotor drives rotation of the pump rotor. Typically, in order to minimize the weight and the size of the turbopump, the common shaft is supported by first and second bearings, the first bearing being closer to the pump and the second bearing being closer to the turbine. The pump and turbine rotors are thus normally cantilevered out respectively from the first and second bearings.
Given the constraints to which turbopumps are normally subjected, in terms of speed of rotation, torque, and vibration, it is normally necessary to lubricate the bearings. A solution that has been generally adopted in the field of turbopumps for feeding propellants to rocket engines, and in particular cryogenic propellants, is to lubricate the bearings with the pumped fluid. Nevertheless, that presents the drawback of normally requiring a sealing barrier between the second bearing supporting the end of the shaft connected to the turbine and the turbine itself. Such a sealing barrier occupies a certain amount of space, thereby increasing the extent to which the turbine is cantilevered out, thereby penalizing the dynamic behavior of the shaft.
It is even more important to achieve sealing between the gas propelling the turbine and the pumped fluid when said gas and said fluid react chemically with each other. In particular, in turbopumps for feeding rocket engines with propellant, the gas propelling the turbine is normally a fuel gas, which generally requires absolute sealing within oxidizer turbopumps in order to separate the pumped oxidizer fluid from the fuel gas propelling the turbine. Under such circumstances, proposals have been made to lubricate the second bearing, i.e. the bearing supporting the shaft beside the turbine, not with the fluid that is pumped by the turbopump, but with a fuel fluid, and to separate this fuel fluid from the pumped oxidizer fluid that also lubricates the first bearing beside the pump, by using a dynamic gasket around the shaft between the two bearings, with an inert fluid being injected therein so as to provide absolute separation between the oxidizer and fuel fluid. That solution is nevertheless complex and difficult to incorporate in a turbopump of small dimensions. In addition, it does not spare the turbopump from the need to incorporate another sealing barrier between the second bearing and the turbine, with the drawbacks as mentioned above.